Keyed cargo container



G. R. PRINGLE KEYED CARGO CONTAINER Feb. 2l, 1967 Filed Sept. 4, 1964FIG. 5

I N VENTOR.

ATTORN EYS United States Patent O 3,305,122 KEYED CARGO CONTAINER GordonR. Pringle, Farnham, England, assignor to Esso Research and EngineeringCompany, a corporation of Delaware Filed Sept. 4, 1964, Ser. No. 394,5336 Claims. (Cl. 220-15) The present invention relates to storagecontainers and more particularly to insulated tanks used in the storageand shipment of liquefied gas cargoes at atmospheric pressure and atcryogenic temperatures in tankers and the like.

Practical and economic considerations have dictated the feasibleconditions of transport and storage of liquefied gases. That is to say,the liquefied gases should be maintained at atmospheric pressures andthe storage containers employed should be of relatively large size andcapable of insulating the supercooled cargo from the ambienttemperatures to prevent volatilization thereof. To this end, containersdesigned for the purpose of storing liqueed gases have included a largeinner tank, fabricated from a material such as aluminum or stainlesssteel, which retains its strength and ductility at the eX- tremely lowtemperatures involved, and an enveloping insulated chamber supportingthe tank. One known eX- pedient for the support of such a cargo tankemploys keys and keyways to secure the tank to its supporting structurewhile accommoda-ting contraction of the tank due to the severetemperature changes encountered in normal use.

In accordance with the principles of the present invention, a storagesystem for a liquid gas cargo incorporates new and improved key andkeyway arrangements, characterized by the use of special intermediateheat insulating bearing blocks, between the key and the keyway, as anintegral part of the supporting system. As an important aspect of theinvention, the fit of the key and keyway is maintained substantiallyuniform under all conditions of expansion and contraction of the tank.Accordingly, the dimensions of the key, keyway and intermediateinsulating bearing blocks are proportioned and displaced such that thebearing 'blocks are maintained in uniform contact with both the key andkeyway throughout the entire range lof temperatures to which the cargocontainer 4is -to be subjected. Optimum performance of the supportingsystem is insured by the uniform fit of the key and keyway at alltemperatures.

For a more complete understanding of the present invention and itsattendant advantages, reference should be made to the following detaileddescription takenin conjunction with the accompanying drawing, in which:

FIG. 1 is a side elevational View of a liquefied gas tanker embodyingthe container system of the invention;

FIG. 2 is a plan View of the tanker of FIG. l; and

FIG. 3 is an enlarged, fragmentary, cross-sectional view of aninsulated, keyed supporting system embodying the principles of thepresent invention, taken along line 3 3 of FIG. 1.

Referring to the drawing, the improved cargo container system of thepresent invention is generally indicated by the reference numeral and istypically included as part of the structure of a seagoing vessel such asa tanker 11. The container system includes an inner tank 12, which maybe conventionally filled with a cargo of liquefied gas, such asliquefied methane, through a dome 13 on the deck of the tanker. The tank12, which is constructed from a material such as aluminum or stainlesssteel and possesses adequate strength to withstand the internal stressesinduced by the cold cargoes, is shaped to be housed generally within thecargo hold 14 of the Ship 11 or within an equivalent supporting struc-ICC ture. The cargo hold itself is completely clad with suitable thermalinsulation 20, such as balsa wood, urethane foam or the like, and asshown in FIG. 3, vertical keyways 15 are formed on each of the verticalwalls 16 of the tank 12 by elongate jaw member 17. For balanced supportof the tank, the keyways are disposed along the major planes of the tank12 which pass through the center of gravity of the tank, as shown inFIGS. l and 2. In accordance with the invention, the keyways 15 of thetank 12 are positively keyed to the supporting cargo hold structure 14,at all temperatures and under all conditions` of expansion andcontraction, by means of elongate key members 19 formed thereon andintermediate insulating bearing blocks 21 which, along wtih a taperedinsulating block 26, form an insulating key generally designated lbyreference numeral 25. In the illustrated preferred embodiment of theinvention, the insulating bearing blocks 21 are secured by adhesive orother suitable means to the side walls of the key member 19 and form aneffectively integral part thereof. As shown, the tapered thermalinsulating blocks 26 are constructed of similar material to that used incladding the cargo hold and are secured to the keys 19 by adhesive orother suitable means to become an effectively integral part thereof.

As an important specific aspect of the invention, the insulating plasticbearing blocks 21, which are fabricated fram suitable insulating bearingmaterial such as a composite mixture of urethane foam, Fiberglas, andresin, are disposed and arranged between the jaws 17 and the key members19 for bearing contact therewith throughout Ithe range of temperaturesto which the tank is to be subjected (normal ambient temperature to aslow as -435 F. for a cargo of liquid hydrogen).

Specifically, since the key member 19 is an integral part of the hullstructure of a ship, sufficient thermal insulation therefor must beprovided to maintain it at ambient temperature to prevent undue crackingstresses to be induced therein. Consequently, the key 19;, when properlythermally insulated, will tbe unaffected by the temperatures of thecargo and its width will be constant or fixed. However, the tank 12 willbe subject to great temperature changes and to relatively large amountsof shrinkage causing the separation and contraction of the jaw members17 and the keyway 15 defined thereby. Therefore, it is necessary toprovide bearing blocks of sufficient width to accommodate this movement,as well as to provide sufficient insulation of the key 19 to prevent thecooling and possible cracking of the hull structure.

Accordingly, since the change `in width of the keyway 1S must becompensated for by a like change in width of the insulating bearingblocks, alone, it being understood that the key member dimensions aspart of the hull structure remain fixed, the Arespective widths of thekeyway, key and insulating bearing blocks may be specificallyproportioned, when the specific coefficients of expansion of thematerials are known and the width of either the key or keyway isinitially chosen. More specifically, and in accordance with importantprinciples of the invention, the substantially uniform fit of theinsulated key 25 within the keyway 15 will be ensured when Wi=iWt at orwhen Wk= t2 wt at where:

Wk=width of the key member 19 Wt--width of the keyway 15 formed betweenthe jaws 17 on the tank 3 Wi=width of each bearing block 21at=coeiiicient of expansion of the tank material a=coeicient ofexpansion of the insulating bearing material Furthermore, it has beendetermined that, as a practical limit, the coetlicient of expansion ofthe bearing block must be at least about 2.25 times greater than thecoetiicient of the expansion of the tank material. Therefore, the widthof the key member 19 must be at least one-fourth (0.25) the Width of theinsulating bearing block and the width of the keyway 1S must be at leastabout two and one-fourth (2.25) times the width of each insulatingblock.

Thus, in accordance with the principles of the invention, the width ofthe keyway 15, defined by the distance between the inner faces 26 of thejaw members 17, is specically proportioned in relation to the Width ofthe insulating bearing blocks 21, the Width of the key member 19, andthe respective coeicients of expansion of the insulating material andthe tank material to ensure that the fit of the effectively insulatedkeys 25 is substantially uniform Within the keyways at all temperatures,i.e., that positive bearing contact of the insulating blocks 21 ismaintained with the keyways 15 at all temperatures and under allconditions of expansion and contraction of the tank 12 as well as thesupporting structure.

Accordingly, it should be appreciated that the support of a cargo tank,through keyways formed thereon, by the new and improved insulated keyswhich are in constant Contact with the keyways under all conditions ofexpansion and contraction provides for the safe storage andtransportation of liqueied gases.

It should be understood that the specific construction herein-illustrated and described is intended to be representative only, ascertain changes may be made therein Without departing from the clearteachings of the disclosure. Accordingly, reference should be made tothe following appended claims in determining the full scope of theinvention.

What is claimed is:

1. In a cargo container system for liquefied gases at cryogenictemperatures including an inner rigid tank supported Within an outersupporting structure by a key and keyway arrangement the improvement inwhich (a) said keyway -is of substantially greater widththan said keyand defines predetermined gaps therebetween,

(b) heat insulating bearing blocks each having a width equal to theWidth of said keyway multiplied by the coeicient of thermal expansion ofthe material from which said keyways fabricated divided by the thermalexpansion of the material from which said bearing blocks are fabricatedare located in said gaps and in Contact with said key and keyway.

2. A container system for cryogenic cargoes, comprising (a) an externalsupporting structure,

(b) an internal rigid tank of predetermined geometric configuration,

(c) elongate keyways formed along vertical axes of said tank,

(d) key members formed on said supporting structure,

(e) insulating means disposed between said supporting structure and saidrigid tank completely enveloping said tank,

(i) said insulating means including plastic bearing blocks disposed insaid keyways and in bearing contact with said key members at alltemperatures, said plastic bearing blocks each having a width equal tothe width of said keyway multiplied Iby the coeicient of thermalexpansion of the material from which said keyway is fabricated dividedby the thermal expansion of the material from which said bearing blocksare fabricated.

3. A container system in accordance with claim 2 in which (a) thecoeicient of expansion of said bearing blocks is at least 2.25 timesgreater than the coefficient of expansion of the material of saidkeyways.

4. A container system in accordance with claim 2,

in which (a) the widths of said key members are substantially 0.25 timesthe width of said insulating means.

5. A container system in accordance with claim 2 in which (a) saidplastic bearing material is a composite mixture of urethane foam,Fiberglas, and resin.

6. In la cargo container system for liqueiied gases at cryogenictemperatures including an inner rigid tank supported within an outersupporting structure by key and keyway arrangement, the improvement inwhich intermediate heat expandable bearing blocks having a predeterminedcoeicient of thermal expansion are interposed between said key andkeyway; said bearing blocks each having a Width equal to the width ofsaid keyway multiplied by the coeflicient of thermal expansion of thematerial from which the keyway is fabricated divided by -the coeiiicientof thermal expansion of the material from which said bearing blocks arefabricated, whereby said bearing blocks are maintained in bearingcontact with said keyway and key at all temperatures from ambient tothose of cryogenic temperatures.

References Cited by the Examiner UNITED STATES PATENTS 2,614,856 10/1952Beyer et al. 220-15 2,823,822 2/1958 Altman 220-15 2,896,416 7/1959Henry 220-9 2,905,352 9/1959 Henry 220-9 3,064,612 ll/l962 Gardner etal. 220-15 3,095,107 6/1963 Bergmann 220-15 THERON E. CONDON, PrimaryExaminer. JAMES R- GARRETT@ Examfne

6. IN A CARGO CONTAINER SYSTEM FOR LIQUEFIED GASES AT CRYOGENICTEMPERATURES INCLUDING AN INNER RIGID TANK SUPPORTED WITHIN AN OUTERSUPPORTING STRUCTURE BY KEY AND KEYWAY ARRANGEMENT, THE IMPROVEMENT INWHICH INTERMEDIATE HEAT EXPANDABLE BEARING BLOCKS HAVING A PREDETERMINEDCOEFFICIENT OF THERMAL EXPANSION ARE INTERPOSED BETWEEN SAID KEY ANDKEYWAY; SAID BEARING BLOCKS EACH HAVING A WIDTH EQUAL TO THE WIDTH OFSAID KEYWAY MULTIPLIED BY THE COEFFICIENT OF THERMAL EXPANSION OF THEMATERIAL FROM WHICH THE KEYWAY IS FABRICATED DIVIDED BY THE COEFFICIENTOF THERMAL EXPANSION OF THE MATERIAL